The focus of this invention is on the petroleum industry. People familiar with the art will realize the features of a self-pressurizing soluble alkali silicate-based system can be readily adapted and found useful in industries such as mining and construction. Further the expansion properties may also be used for prevention and correction of subsidence such as in buildings or roadways.
It has been known since the 1920's that soluble alkali silicates such as sodium silicate are an effective means for providing conformance control in a reservoir. The term conformance is a broad term and includes control of excess water production with the goal of improving petroleum recovery and reducing costs. Recently, there has been greater interest in the use of soluble, alkali silicates such as sodium silicate. This resurgence is being driven by the performance properties of soluble alkali silicates as well as the environmentally friendly and low cost nature of sodium silicate.
The chemistry of sodium silicate for conformance has been well documented in the literature. The paper by P. H. Krumrine and S. D. Boyce, Profile Modification and Water Control with Silica Gel-Based Systems, SPE 13578 presented at the 1985 SPE International Symposium on Oilfield and Geothermal Chemistry, Phoenix, Ariz., Apr. 9-11, 1985 is a leading article on the subject. This paper presents the chemistry, properties, benefits, limitations, and methods associated with sodium silicate conformance and provides an extensive list of potential setting agents. This paper is incorporated herein by reference. Also documented have been the use of fillers and bridging materials within a soluble metal silicate. Generally accepted features of soluble alkali silicate systems include;                initial low viscosity (1-2 centipoise) which promotes penetration        small molecular weight which promotes penetration        excellent thermal stability        excellent chemical stability        high strength on setting        flexible set times (instant to several days)        environmentally friendly        moderate to low cost        
Commonly cited constraints of soluble alkali silicate-based technology include;                gels can show syneresis (i.e. prone to shrinking)        the gel is rigid and prone to fracture        
The issue of shrinking/contraction is not exclusive to sodium silicate and is known to occur in polymer as well as cement systems. The lack of a tight seal can result in poor zonal isolation leading to gas migration, gas entrapment, and/or excessive water production among other issues. In the case of cement, several methods have been proposed to offset shrinkage. One such technique is the use of gas generating additives. When a suitable metal is added to the cement slurry, the high pH environment results in the production of hydrogen gas. This technology is described in U.S. Pat. Nos. 3,197,323; 3,579,366 and 3,709,707 for use in structural concrete compositions to offset contraction as well as the tendency to settle. The use of gas generating additives for oilwell cement was described by Carter et al: Expanding Cements for Primary Cementing, Journal of Petroleum Technology, May 1966. This article describes the use of zinc, magnesium, iron and aluminum powders to prepare expansive cements. The metal powders react in a cement slurry to produce minute bubbles of hydrogen. U.S. Pat. No. 4,304,298 describes an improved oil well cement slurry for the generation and entrainment of gas. U.S. Pat. No. 8,689,871 describes the difficulty of high reactivity of metals when exposed to a cement slurry and the coatings that may advantageously delay the gas generation reaction.
Unlike cement which sets via a hydration reaction, soluble silicates set via a gelation/polymerization reaction caused by a loss of alkalinity. Soluble silicates can also be set via a precipitation reaction with metal cations. Soluble silicates may also be made to set via a dehydration reaction where the loss of water causes the soluble silicate to thicken and eventually revert back to a glass. The setting mechanisms of soluble silicate function to prevent fluid loss. Alkali silicates may also donate their charge which can react with solid material in the plug and also function as a setting mechanism.